A manner of information registration has been conventionally employed in a field of merchandise distribution in which bar codes are attached to commodities and these bar codes are read by a bar code reading apparatus (bar code scanner) so that information concerning the commodity such as a price or name thereof is registered in a register.
The bar codes attached to the commodities are arranged in such a manner that the information concerning the ordinary commodities are coded and the coded information can be represented by an array of width information of respective black bars or white bars constituting the bar code (an integer number ratio of a width of respective white and black bars constituting the bar code). In the bar code reading apparatus, as for example shown in FIG. 70(a), a bar code 200 attached to such a commodity is exposed under an irradiation of a beam of light 201 such as a Gaussian beam, and an intensity variation signal 202 of the beam of light (see FIG. 70(c)) reflected on the surface of the barcode is received so as to read data represented by the variation of intensity contained in the intensity variation signal. The amplitude value of the intensity variation signal 202 is dependent of a color of respective bars constituting the bar code.
The bar code reading apparatus as described above may have an outward appearance shown in FIG. 57. The bar code reading apparatus is classified into several types in one of which a beam of light generated by an LD (Laser Diode) or the like scans the bar code and a reflected ray of light thereof is examined to detect the white-black pattern of the bar code. Another type of the bar code reading apparatus is that an external ray of light generated by a CCD (Charge Coupled Device) or the like is irradiated on the bar code to detect the white-black pattern of the bar code. In a conventional bar code reading apparatus, whichever types the apparatus belongs to, a ratio of width of the white bar and black bar constituting the bar code (module ratio) is calculated in accordance with the following procedure (of [1] to [4]).
[1] To receive the ray of light reflected on the bar code by an light receiving element so that the light receiving element generates an electric signal having an amplitude corresponding to the intensity of the ray of light.
[2] To extract from the amplitude variation of the light-received signal a boundary signal (edge signal) representing a boundary of transition from the white bar to the black bar or a boundary of transition from the black bar to the white bar which constitute the bar code.
[3] To measure the extracted edge signal distance by using a clock having a resolution of several tens times to several hundreds times the bar width as a bar width count representing the edge signal distance.
[4] To determine the width of respective bars constituting the bar code based on the measured count, thereby to calculate a width ratio of the white-black bars.
FIGS. 58 and 59 are block diagrams showing a conventional bar code reading apparatus, for example. As shown in FIG. 58, a bar code reading apparatus (see U.S. Pat. No. 5,061,843) is an apparatus for reading bar code information by carrying out a signal processing mainly composed of analog processing, and arranged to include an optical scanning section 102A, and analog processing unit 102B and a digital processing unit 102C.
According to the bar code reading apparatus shown in FIG. 58, a beam of light generated by an LD 102a-1 of the optical scanning section 102A is led to a polygon mirror 102a-2, and with the rotation of the mirror the beam of light is made to scan the bar code 102 in a direction from the left end to the right end thereof (in the figure, direction from a to b), for example, with the result that respective black bars or white bars are exposed under the beam of light.
The beam of light scanning the bar code 102 on the surface thereof is reflected with an intensity which corresponds to the width of the black and white bars constituting a pattern of the bar code. The intensity of the reflected light beam is dependent of the color of the respective bars of the bar code. That is, if the light beam reflects on a white bar then the light beam comes to have a relatively large intensity while if the light beam reflects on a black bar then the light beam comes to have a relatively small intensity.
That is, when the laser beam is made to scan the bar code 102, the returning light comes to have a signal waveform which is characterized by having a small amount of luminous energy upon scanning a black bar while having a large amount of luminous energy upon scanning a white bar (see Sig 10, 50e, 50f in FIG. 60).
As for example shown in FIG. 60, the bar code reading apparatus introduces into the apparatus, an electric signal (see Sig 11) having an amplitude value which derives from detection on the above-described intensity variation of the reflected light beam (represented by reading of the signal Sig 10 on ordinate of FIG. 60), and thereafter the apparatus carries out a signal processing on the electric signal, whereby the bar code information can be read. The above-described signal processing is carried out in the following steps of (1) to (4).
(1) A laser light beam generated from the LD 102a-1 is made to scan the bar code 102 and the reflected light beam thereof is photo-electrically converted into an electric signal.
(2) In an analog processing section 102B, an amplifying unit 102c effects a necessary amplifying processing on the electric signal deriving from the photoelectric conversion, and thereafter the amplified electric signal is subjected to a differentiation processing in a one-time differentiating unit 102d. That is, the photoelectric converted signal is differentiated to obtain a differentiated signal waveform 50j (signal Sig 12) having a peak at a boundary between a white bar and a black bar. This signal is added with a minute time delay to create another signal 50k (signal Sig 13).
This differentiated signal (signal Sig 12) and the signal having added with a delay by the delaying processing unit 102e (signal Sig 13) are compared with each other to form the differentiated signal into an edge signal having an edge at a point corresponding to the peak in the differentiated signal. Then, the edge signal is converted into a digital signal. That is, a positive peak of the differentiated signal corresponds to an edge signal deriving from a change from a black bar to a white bar (WEG, see a signal Sig 14) while a negative peak of the differentiated signal corresponds to an edge signal deriving from change from a white bar to a black bar (BEG, see a signal Sig 15).
In other words, when the signal 50j (Sig 12) and the signal 50k (Sig 13) are compared with each other by the comparator 102f, the edge signal WEG generated upon change from the black to the white and the edge signal BEG generated upon change from the white to the black can be obtained.
Meanwhile, in order to prevent an undesirable edge generation at a portion 50s in which no differentiating response is present, there is provided a circuit gating an edge signal which is created when the differentiated signal 50j stays within a constant rate level 501 of the differentiated signal 50j itself.
(3) In a width measuring unit 102g of a digital processing section 102C, edge signal distances of a bar image signal (i.e., a distance between a BEG and a WEG sequel to the BEG and a distance between a WEG and a BEG sequel to the WEG) are measured by a count of a clock 102h or the like (see signal Sig 16). The clock 102h for measuring the time distance between the pair of edge signals shall have a sufficient resolution.
(4) In a module calculating unit 102i, a module number expressed as respective bar width data is calculated as a proportional calculation based on the count delivered by the width measuring unit 102g (see signal Sig 17).
Ordinarily, code information expressed as a width information on a bar code is composed of integer number ratio data having a predetermined length known as a module as an unit. Each of the bar has a width of an integer multiple of the above-described module. In this case, the integer number ratio is obtained based on the bar width value by the width measuring unit 102g so as to find the module ratio.
Further, as shown in FIG. 59, an AD (Analog-Digital) converter 103d is provided to convert the acquired electric signal in the form of analog signal into a digital signal. The above-described signal processing shown in FIG. 58 can be carried out in the following steps of (1) to (5). According to the arrangement of the bar code reading apparatus shown in FIG. 59, signal processing is carried out in a digital manner in blocks corresponding to the blocks (see blocks identified by reference numerals 102d, 102e and 102f) of the aforesaid bar code reading apparatus shown in FIG. 58 in which the signal processing is effected in an analog manner.
(1) Similarly to the case of the bar code reading apparatus of FIG. 58, a laser light beam generated from an LD 103a-1 is utilized for scanning a bar code 103 by using the rotation of a polygon mirror 103a-2, whereby a reflected light beam from the bar code 103 is received by a light receiving unit 103b and an optical signal is photoelectric-converted into an electric signal.
(2) An amplifying unit 103c effects a necessary amplification processing on the electric signal supplied from the light receiving unit 103b, and thereafter the resulting signal is sampled in a digital manner by the A/D converter 103d or the like.
(3) A digital signal from the A/D converter 103d having added with a time delay difference by delaying units 103e and 103f is subjected to a differential processing in differential processing units 103h and 103i. 
That is, the differential processing unit 103h compares a signal from the A/D converter 103d and added with a delay time of t2 and the same signal added with a delay time of t1 with each other, and outputs a result as a compared result signal A. Further, the differential processing unit 103d compares a signal from the A/D converter 103d and added with a delay time of t1 and the same signal added with no delay time t0 with each other, and outputs a result as a compared result signal B.
(4) A comparator 103i compares difference signals supplied from the differential processing units 103g and 103h with each other so as to detect a point at which the largest variation is brought about and the output polarity is changed, and this point is outputted as an edge point.
(5) Similarly to the case of the width measuring unit 102g of aforesaid FIG. 58, a width measuring unit 103j counts a distance between edge points by using a clock 103k. 
As described above, the code information expressed as width information on the bar code is composed of integer number ratio data made of a predetermined length unit known as a module. In both of the bar code reading apparatus shown in FIGS. 58 and 59 based on the conventional technology, measurement is made on the integer number ratio data by counting the edge signal distance by using a clock.
In the conventional bar code reading apparatus shown in FIG. 58, however, if the bar code 102 has a blurred portion in printing, a concave-convex portion on the sheet of paper thereof (see portion shown at reference 50c in FIG. 60) or the like, for example, such portion will cause a distortion in a waveform representing the luminous energy of the returning light beam (see reference 50g), with the result that even in the differentiated signal two peaks having a positive value are created continuously (see reference 50h and 50i).
If the edge signal is created from the differentiating signal, two edge signals of the same kind will be created continuously. Therefore, when the bar width is counted in a final step, it follows that the count is made by using a false edge. Consequently, the count indicating the bar width will have an error (50q, 50r) relative to the inherent true value (see reference 50o, 50p).
If calculation is made to obtain the integer number from the bar width value and the error is equal to or more than 0.5 module (in this example, the error is just equal to 0.5 module), erroneous recognition will be caused in the result of reading the bar code information.
This erroneous recognition in the result of reading the bar code information due to the blur or the like on the bar code is mainly caused by the wide band characteristic of a circuit section including the light receiving unit 102b, amplifying unit and the differentiating unit, and the laser beam diameter. That is, as shown in FIG. 62, the arrangement of the bar code reading apparatus tends to have a characteristic that the scanning speed v is made slow to attain proper laser scanning at a window 57a while the depth of field for reading is made deep (L→large) to make the beam scanning speed v fast.
That is, when a bar code is brought close to the window 57a to carry out reading operation, then a distance between the LD 102a-1 or the polygon mirror 102a-2 and the bar code will become relatively short and the depth of field for reading will become shallow (L→small). However, if the reading operation is carried out with the bar code remote from the window 57a, then the distance between the LD 102a-1 or the polygon mirror 102a-2 and the bar code will become relatively long and the depth of field for reading will become deep (L→large).
Accordingly, as shown in FIG. 61, it is requested for the circuit characteristic to have a wide band characteristic capable of covering from a low signal band (see reference 51b) in which the beam scanning speed is slow and the bar code to be read is large to a high signal band (see reference 51c) in which the beam scanning speed is fast and the bar code to be read is small.
As a consequence, when a bar code having a relatively large magnitude is made to scan near the window surface, a minute laser beam will pickup the aforesaid printing blur or an abrasion to yield an erroneous recognition.
Moreover, as an influence from the beam diameter, for example, a light beam generated from the LD 102a-1 will be scattered as the depth of field for reading becomes deep. Thus, it becomes difficult for the light beam having a large diameter to accurately detect the reading bar code width with the reflected light beam thereof.
What described above will be summarized as follows. That is, the above-described bar code reading apparatus shown in 58 encounters difficulties of (1) to (4) listed as follows.
(1) In order to make the apparatus capable of processing a bar code signal deriving from a reading operation effected at a depth of field for reading L which can extend from a shallow point to a deep point, a circuit on the receiving side is requested to have a wide band frequency characteristic. Therefore, the amount of noise will be increased as the band is set to be wide, which fact will cause a problem that a signal to noise ratio (S/N) will be deteriorated.
(2) Since the apparatus is requested to read a fine bar code, the laser beam is also requested to have a thin diameter. In this case, if the bar code has a concave/convex portion on the sheet of paper thereof or a blurred portion or the like on the bar thereof, this concave/convex portion will be picked up and the signal will reflect the concave/convex portion. As a consequence, a boundary signal representing the boundary between a white bar and a black bar can be generated at a point other than the desired point. This fact can cause an erroneous recognition of an edge between the white bar and the black bar.
(3) Since the scanning is made by a laser light beam, deeper the depth of field for reading becomes, wider the beam diameter. Thus, the laser light beam cannot provide high resolution, and hence there can be a case that to read a label of a fine bar code becomes difficult.
(4) When an edge signal is extracted, the signal will function as a bar image signal representing white or black of the bar code. In order to measure the width time of the bar image signal, the clock for counting the width time must have a time period short enough with respect to the bar width time. For this reason, a hardware operating at a high clock rate can become expensive and it might be requested to take a counter measure against an EMI (electromagnetic interference).
Also the above-described bar code reading apparatus shown in FIG. 59 will encounter problems similar to those of (4) and (5) which are described with the aforesaid bar code reading apparatus shown in FIG. 58. In addition, the same bar code reading apparatus will encounter problems of (1) and (2) which will be described in the following.
(1) In order to keep a bar width accuracy, the A/D converter is requested to have a high sampling frequency (equal to or more than about ten times the minimum reading bar width). For this reason, the signal frequency band is increased and the reading system of the apparatus will become more sensitive to a noise caused by the above problem or a noise deriving from a circuit thereof. Thus, an edge between the white and black portions of the bar width can be erroneously recognized.
(2) As described above, the data shall be sampled at a high rate. When the resulting data is utilized up to the final step, a processor is requested to have a high performance capable of processing a large quantity of sampled data. Moreover, a larger memory is also requested to store the large quantity of sampled data.
The present invention is made in view of the above aspect. Therefore, it is an object of the present invention to provide a method of reading information and an apparatus therefor, a method of acquiring a signal for use in an information reading apparatus, a method of processing band limitation, a method of extracting a timing point amplitude and a method of processing a signal thereof, a read signal processing unit, and a method of processing the read signal and a processing unit thereof, which makes it possible to suppress the size of hardware and a price thereof and to improve an S/N ratio of a reading signal and reading resolution, wherein even if depth of field for reading is enlarged or a concave/convex portion or a blurred portion is left on the reading face, reading precision can be improved.